The invention relates to a structure for printed circuit design and, more specifically to a substrate structure for surface mounted components or devices which eliminates or substantially reduces the need for vias directly beneath the surface mounting site.
Array surface mounted devices such as ball grid array packages (BGAs, PBGAs, CBGAs, TBGAs, etc.), chip scale packages (CSPs), and direct chip attach (flip chips) are being used to achieve better performance in system miniaturization. However, these types of devices have large numbers of contacts or balls for contacting conductive pads of a substrate, and each pad must be routed for interconnection with various components and test point vias. As shown in FIG. 1, this routing adds to the layer count of the substrate, and further requires a potentially large number of vias underneath the package.
This conventional routing and via configuration adds to manufacturing costs, and further provides for additional connections which are subject to potential failure such as during the manufacturing process.
The need remains for a cost-effective and reliable method for connecting array surface mounted devices to substrates.
It is therefore the primary object of the present invention to provide a substrate structure for mounting array surface mounted devices wherein vias directly beneath the device are reduced or eliminated.
It is a further object of the present invention to provide a substrate structure for surface mounting such devices which results in a reduction in the number of layers as compared to conventional dielectric substrate constructions.
It is still another object of the present invention to provide a substrate structure as described above which is less expensive and more reliable.
It is a still further object of the present invention to provide a substrate structure having improved solder joint reliability.
It is another object of the present invention to provide a substrate structure wherein single substrate layers can be defined as ground planes, voltage planes and the like.
Other objects and advantages of the present invention will appear hereinbelow.